Nextcloud service discovery not fully working

Question

I have a nextcloud instance on shared hosting.

Unfortunately I cannot use it for cal-/carddav because (only) macs cannot seem to find the offered services.

Since a few versions, the nextcloud administrative interface tells me, that service discovery is not working correctly. While dav responds as such on the links provided by the calendar and contacts app, the .wellknown links necessary for some clients (macs) redirect to the default files view.

The very installation sets the redirects exactly the way, the nextclouds' troubleshooting docs tell me to.

<IfModule mod_rewrite.c>
  RewriteEngine on
  RewriteCond %{HTTP_USER_AGENT}  DavClnt
  RewriteRule ^$         /remote.php/webdav/          [L,R=302]
  RewriteRule .* - [env=HTTP_AUTHORIZATION:%{HTTP:Authorization}]
  RewriteRule ^\.well-known/host-meta /public.php?service=host-meta [QSA,L]
  RewriteRule ^\.well-known/host-meta\.json /public.php?service=host-meta-json [QSA,L]
  RewriteRule ^\.well-known/webfinger /public.php?service=webfinger [QSA,L]
  RewriteRule ^\.well-known/carddav /remote.php/dav/ [R=301,L]
  RewriteRule ^\.well-known/caldav /remote.php/dav/ [R=301,L]
  RewriteRule ^remote/(.*) remote.php [QSA,L]
  RewriteRule ^(?:build|tests|config|lib|3rdparty|templates)/.* - [R=404,L]
  RewriteCond %{REQUEST_URI} !^/\.well-known/(acme-challenge|pki-validation)/.*
  RewriteRule ^(?:\.|autotest|occ|issue|indie|db_|console).* - [R=404,L]
</IfModule>

See the two caldav and carddav lines?

Still, something is off with these rewrites. What could it be?